Our customer produced a UHF transmitter used for data telemetry that had some undesirable characteristics. AO was hired to investigate the problems and redesign the transmitter.


The initial task was to remove a persistent unwanted 800MHz harmonic signal in the nominal 401MHz transmitter output. We determined it was due to excessive harmonic content in the output of a phase-locked oscillator that generated the transmitter's operating carrier signal. When the origin of the spurious signal was determined a harmonic supression filter was implemented in a revision of the circuit board artwork.

Next we eliminated several circuit adjustments from the manufacturing process. At the time of the original design work that produced this transmitter, a decision had been made to use variable capacitors to tune stages of the tranmitter's signal chain at three points. In practice it was found that this adjustment was time-consuming, and the UHF variable capacitors were relatively expensive. We analyzed the operating Q of these tuned circuits and specified inductors and capacitors having precision sufficient to meet the transmitter's performance specifications without a need for adjustment of the three interstage tuned circuits. This change made the device less expensive to manufacture, and shortened the acceptance-testing process.

Next we redesigned the UHF-RF and microprocessor control circuit boards to improve manufacturability. This telemetry transmitter was implemented using surface-mount component technology. The original work used accepted standards for PCB design, but the resulting PCB was difficult to inspect for proper soldering. It had very small clearance areas around the components and tiny solder pads which provided no visible solder fillet. Small adjustments to these details made a considerable improvement in the success of post-soldering inspection of the PCB assemblies.


This combination of small changes improved performance and enabled much more-efficient production of the product.